Directive radio antenna



Oct. 26, 1948. H. BECKER DIRECTIVE RADIO ANTENNA Filed Dec. 24, 1942 RADIO TRANSMITTER AND RECEI VE R Inventor Howard 1. Becker,

by Hi5 Attorney.

Patented Oct. 26, 1948 DIRECTIVE RADIO ANTENNA Howard 1. Becker, Schenectady, N. Y., assignor to General Electric Com New York pony, a corporation of Application December 24, 1942, Serial No. 469,986

My invention relates to directive radio antennas, and more particularly to directive antennas for use in conjunction with radio direction flnding equipment.

One of the objects of my invention is to provid new and improved means for sweeping an electromagnetic beam over a predetermined desired path.

The invention also has for its object the provision of a new and novel means and method for shifting a radio beam through wide angles without necessitating continuous movement of the entire directional apparatus. A

It is a still further object of my invention to provide new and novel means of small mass for continuously sweeping an electromagneitc beam over a large area.

It is another object of my invention to provide means for using a portion of a radio beam continuously to sweep an area appreciably larger than that covered by the main beam and without moving the main beam.

My invention also has for its object the provision of a method for centering a radio beam on an object without continuously oscillating the main beam.

My invention itself will be more fully understood both as to its organization and method of operation, together with further objects and advantages thereof, by reference to the following detailed specification taken in conjunction with the accompanying drawings in which Fig. l is a diagrammatic representation of a radio direction finding apparatus embodying my invention in one form; Figs, 2 and 3 are perspective views of directional antennas for such a system embodying my invention in modified form; Fig. 4 is a sectional view of another form of my invention; and Figs. 5 and 5a and 6 and 6a. illustrate still further embodiments of the invention.

Referring now to the drawings, and particularly to Fig. 1, I have illustrated a radio direction find ing equipment comprising a radio transmitter and receiver I ll connected through a transmission line H to a dipole antenna l2 positioned at the focal point of a metallic reflector l3 of paraboloidal configuration. By way of example only I have chosen to illustrate the invention as applied to a radio wave transmitter and receiver connected to a single antenna. However, I wish to have it understood that the invention is not limited in its broader aspects to a single antenna for both transmission and reception. If desired separate transmitting and receiving antennas may be used, The wave transmitter and receiver It is illus 6 Claims. (Cl. 343-16) 2 trated only in block form, but it will be understood by those skilled in the art that this apparatus comprises a suitable high frequency wave generator connected to the dipole antenna ii for the transmission of a beam of electromagnetic waves in the direction determined by the reflector it. The apparatus it] also comprises a sensitive radio receiving apparatus which is operatively connected to the antenna it during null periods of transmission for the purpose of indicating, as for example upon a cathode ray tube, the reception by the antenna I! of echo waves received .face of a perfectly conducting material.

from any object which may be found in the path of the transmitted beam. Since the high intemlty transmitting apparatus and the sensitive receiving apparatus are shown both connected to the common antenna l2 and thus to each other, it will be understood that the apparatus It! also includes suitable means for protecting the receiver against waves originating in the transmitter and supplied directly to the receiver.

It is known that high frequency radio waves, such as those emanating from the dipole antenna; 82, possess certain of the properties of light. Among these properties are rectilinear propagation and'reflection. It is also known that such radio waves are reflected in the manner of light and with substantially no distortion from the sur- Most common conducting metals, such as copper, serve as substantially perfect reflectors of electromagnetic waves. Accordingly, it will be understood that the presence of a paraboloidal reflector i3, which may for example be made of copper, will direct the waves from the antenna l2 in the direction toward which the paraboloid faces and substantially parallel to the axis of the paraboloid. At Fig. 1, I have shown a planar metallic reflector, such as a flat copper sheet l4, pivotally attached at its center to a motor driven shaft i5 for rotation about the axis of the shaft. The shaft i5 is driven through suitable gearing by a motor 15a mounted upon the paraboloid ill. The pivotal attachment of the reflector It to the shaft permits adjustment of the angle between the shaft and the plane of the reflector. Preferably this angle is adjustable between zero and 45 degrees. By way of example I have shown the reflector M disposed at a small angle to the shaft i5 so that when the reflector is in the position shown, the transmitted beam follows the path indicated at It. It will now be understood that when the reflector it is rotated by the shaft l5, the beam l6 traces a conical path. The broken lines l'l indicate the position of the beam when the reflector is rotated a suitable ,mount to a position ii, 180 degrees displaced from the position shown.

The paraboloidal reflector I3, carrying the antenna i2 and the reflector M, is rotatably mounted upon a horizontal'shaft Ha carried in I322. The mount lib is mounted upon a base I3c which is rotatable about a vertical axis. Suitable reversible electric motors led and Ne are provided for rotating the paraboloid it about the shaft "a and rotating the mount'i3b about its vertical axis thereby to provide elevation and azimuth adjustments, respectively, of the electromagnetic beam. Manually operable means such as hand cranks or the like may of course be usedin place of the motors i311 and idea if desired.

In the operation ofthe device of Fig. 1, the radio beam is continuously swept through a conical path at any desired angle determined by the angular position of the reflector l4. As soon as a reflected or echo wave is received the paraboloidal reflector i3 is moved to bring the axis of the paraboloid nearer the object. This direction is known from the characteristic of the indication on the cathode ray device forming part of the receiver indicated at M. While it is no part of the instant invention, it may be briefly mentioned that it'is well known to give directional senseto a rotating radio beam by suitable commutating apparatus synchronized with the movement of the beam. Commutating ap-= paratus of this general type is shown applied to a magnetic induction indicator in Patent 2,277,905, issued to Warren S. Eaton on March 31, 1942. Through this commutating apparatus the quadrant in which a reflecting object appears is apparent from the position of the indication on the cathode ray tube or other indicating device. Accordingly, the entire apparatus i2, it, it is moved to bring the axis of the beam nearer the object until the indication is equal in all four quadrants of beam sweep. This movement may be effected either manually or automatically in response to the directional indication on the receiver. An equal reflected pulse in all four quadrants indicates that the object is centered on the axis of the paraboloid. If it is desired to center the beam even more accurately, the angle between the reflector i4 and the shaft I 5 may be gradually diminished to decrease the radius of sweep while maintaining the beam centered. After the beam is centered on theobject the reflector M is placed at a. zero angle with the shaft l5 and its rotation stopped if desired. The beam may then be kept centered by any known manual or automatic tracking apparaus for moving the paraboloidal reflector I 3 and main beam to follow the object. While such automatic tracking apparatus forms no part of the instant invention, a suitable electric control system for so controlling the motors [8d and l3e is described and claimed in a copending application, Serial Number 414,126, filed October 8, 1941, by Sidney Godet, n-ow patent 2,412,612, issued December 17, 1946, and assigned to the same assignee as the instant application. The beam may of course be kept centered by direct manual control of an operator.

At Figs. 2 and 3, I have shown arrangements for sweeping one half of the beam through a vertical angle and the other half of the beam through a horizontal angle. As illustrated at Fig. '2, this arrangement comprises a planar metallic reflector is having one edge pivotally mounted substantially along a diameter of the circular face of the paraboloidal reflector, and a second planar metallic reflector 20 having one edge pivotally mounted perpendicular to the pivotal axis of the reflector I9 and along a radius of the face of the paraboloidal reflector. Any suitable mechanism may. be provided for continuously oscillating the planar reflectors I! and 20 about their pivotal axes. As indicated at Fig. 2, such oscillationof the reflectors will cause the upper half of the beam to be swept through a vertical angle a and the lower half of the beam to be swept through horizontal angles 0; upon either side of the parabolic axis.

In the operation of the arrangement of Fig. 2 the beamniay be centered after detection by first stopping vibration of both vertical and horizontal deflectors. If the object still appears it is known to be on the main beam. If the object does not appear the vertical reflectors alone may be set in operation. If the object appears again the entire paraboloid may be raised until the object comes into the main undeflectedbeamr If the vertical deflection alone does not detect the object the horizontal deflectors alone may be operated and the paraboloid [3 moved in the proper direction to center the beam. It will be understood that this process may be continued until an equal indication is received in the two horizontal and one vertical sweep areas.

It will also be understood by those skilled in the art that, if desired, conventional methods of centering may be used after the object has been brought into the main beam by use of my invention. I have described above methods of com tering by use of my planar reflectors alone, but, if desired, well known means for eccentric rotation of the antenna or paraboloid focus may be used for centering after locating the object in the main undeflected beam.

The devices of Figs. 1 and 2 have been described primarily to illustrate certain of the fundamental aspects of my invention. While these embodiments possess certain advantages, it will be recognized that the planar reflectors necessary for deflecting the entire beam at the small angle ordinarily desired are of size larger vibrating mechanism 24.

than is desired in many applications. vice of Fig. 3 avoids this difliculty and is a more practical arrangement in such applications for sweeping half of the beam horizontally and half vertically in the manner illustrated at Fig. 2. According to Fig. 3 a plurality of relatively small planar metallic reflectors 2i are pivotally mounted on horizontal axes in the upper half of the beam, and a plurality of planar metallic reflectors 22 are pivotally mounted on vertical axes in the lower half of the beam. As indicated in the drawing, the reflectors 2| may suitably be connected together and to a suitable vibrating mechanism 23, while the reflectors 22 may be connected together and to a second It will be understood that preferably the reflectors of each groupli and 22 are positioned sufllciently far apart so that, when disposed at the angle of maximum deflection, the rays reflected from any one of the reflectors do not impinge upon the adjacent reflector. If such double reflection took place, the emanated ray would simply be parallel to and displaced from the axis of the paraboloid. It will be understood that the operation of the device of Fig. 3 is entirely similar .to that of the device of Fig. 2.

According to my invention sweeping may also be accomplished by using only a portion of the The de- 1 accuses 4, I have shown such an arrangement as a modi- I flcation of the device illustrated at Fig. 1. Ac-' cording to Fig. 4 a relatively small planar metallic reflector 25 is adjustably mounted upon a motor driven shaft 26 and is normally so disposed and of such a size that its projection upon the plane of the face of the paraboloidal reflector 83 covers only a relatively small portion of the face. The angular position of'the reflector 2b with respect to the shaft 28 may be adjusted as desired by any suitable means, such as a set screw 25a. With this arrangement the main beam 27 is undisturbed, while a second beam 2d, produced by deflecting small portion 28 of the main beam, is swept in a conical path about the beam 21. In the operation of the device of Fig. 4 the sweeping beam 28 is moved continuously in its conical path until an echo pulse from a distant object is received in the receiving apparatus. The receiving apparatus may be provided with a. suitable commutating arrangement synchronized with the movement of the 1 reflector 28 to indicate from which quad-rant the reflection is being received. After a reflected wave is received, the reflector is first stopped to determine whether the object is in the main beam or in the area swept by the beam 28. If the object is found to be outside the main beam, the reflector i3 is moved to bring the main beam onthe object. The reflector 25 is then pivoted upon the shaft 26 until its plane is brought more nearly into coincidence with the axis of the paraboloidal reflector it. By this movement the sweeping beam 28 is gradually brought entirely within the main beam. The sweeping of the beam 28 entirely within the main beam gives a sense of direction of the object which is now also within the main beam. The directional sense arises from the relative intensities of the reflection in the four quadrants of the sweeping beam. .Now the main beam may be moved to center it on the object as indicated by obtaining reflections of equal intensity in all quadrants. Finally the angle between the reflector 25 and the shaft 26 is brought to zero asin the manner described heretofore in connection with Fig. 1. After the main beam is centered on the distant object, it may be retained at the center by any suitable manual or automatic tracking apparatus well known to those skilled in the art and formmg no part of the present invention.

At Figs. 5 and 5a, is shown another embodimerit of my invention in which the main portion of the beam normally remains fixed and only a portion of the beam is used for sweeping. According to the modification of Figs. 5 and 5a, a group of relatively small parallel reflectors 29 are pivotally mounted on horizontal axes to deflect a portion of the upper half of the beam through a vertical sweep angle, and a group of small parallel enclosed metallic reflectors 30 are pivotally mounted upon vertical axes to sweep a portion of the lower half of the beam through a horizontal angle. The reflectors 29 are connected together and to a suitable vibrating mechanism 3i, and the reflectors 30 are connected together and to a second suitable vibrating mechanism 32. Fig. 5c is a cross sectional view of the device of Fig. 5 to illustrate the manner in which a portion 6 of the upper half of the beam is deflected vertically by the reflectors 29.

The operation of the arrangement of Figs. 5 and 5a in locating and centering the beam upon a remote reflecting object will be readily understood from the foregoing descriptions of the operation of the devices of Figs. 2 and 4. The device of Fig. 5 operates in the same manner as that of Fig. 2 until the main beam is centered upon the object. Thereafterthe operation is fundamentally similar to that of Fig. 2 but is characterized by a directional sense within the main beam as a result of sweeping a small portion of the beam. as in Fig. 4.

The modification of Fig. 6 is similar to that of Figs. 5 and 5a except that each quadrant of the circular space of the paraboloidal reflector i3 is I provided with a group of reflecting vanes. As shown at Fig. 6, the two groups of reflecting vanes 36 in the upper quadrant are vertical reflectors and are connected to a vibrating mechanism Na. and the two groups of vanes 35 in the lower quadr-ant are horizontal reflectors and are connected to a vibrating mechanism am.

As previously mentioned in connection with Fig. 2, it may be desirable to center the beam after the object has been brought into the main beam by rotation of the dipole antenna about the focal point of the paraboloidal reflector. Such an arrangement is shown at Fig. 6a where the dipole I2 is mounted upon one side of a. dentrally positioned motor driven shaft 35. In all other respects the modification of Fig. 6a is similar to that of Fig. 6. It will be understood of course that rotation of the dipole for centering is not necessary to the operation of the devices of either Figs. 2 orfi, and that the device of Fig. 6 may be operated for centering in the same manner as Fig. 5. On the other hand, the rotatable dipole may be used with any of the forms of the invention shown.

In the foregoing description reference is made to echo waves as waves reflected from an object in the path of the directed beam. It will of course be understood that in certain applications, such as aircraft recognition, the directed beam may be received in suitable receiving apparatus located at the object, such as an airplane, and relayed by separate transmitting apparatus upon the plane back to the point from which the beam is transmitted. It will thus be understood that in the claims appended to this specification the term echo, wherever used, is intended to include both a reflected wave and a separate wave transmitted by apparatus associated with the object.

From the foregoing description it will be evident that my invention provides means whereby a directional electromagnetic beam may be swept out the complication of the multiplicity of dipoles necessary in antennae wherein selected pairs of adjacent dipole antennas'are sequentially energized to produce a desired pattern of beam movement. In a preferred form of the invention only a portion of the beam is swept in a predetermined path around the main beam until an object is located, and the beam is thereafter centered by progressive decrease of the angle of sweep. Where the primary beam directing apparatus is a relatively bulky paraboloidal reflector, the invention has the advantage that the moving beam deflecting parts are of substantially smaller mass than the paraboloid so that the beam may be swept more rapidly and with less danger of deterioration of the entire apparatus due to vibration.

While I have illustrated only certain preferred embodiments of my invention by way of illustration, many further modifications will occur to those skilled in the art. Accordingly, I wish to have it understood that I intend by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a radio direction finding a paratus, means comprising an antenna for unidirectionally projecting a beam of electromagnetic waves into a desired area, means for receiving echo waves from an object in the path of said projected beam, a plurality of movable planar reflectors positioned in the path of said projected beam to deflect at least two portions of said beam, and means for moving said reflectors continuously to sweep said portions of said beam through separate predetermined paths to define said area.

2. In a radio direction finding apparatus, means comprising an antenna for projecting a beam of electromagnetic waves into a desired area, means for receiving echo waves from an object in the path of said beam, pivotally mounted planar reflecting means positioned in the path of a first portion of said beam and spaced from said projecting means for deflecting said portion of said beam in one direction, second pivotally mounted planar reflecting means positioned in the path of another portion of said beam for deflecting said other portion to said beam in a second direction, and actuating means for continuously moving said reflecting means to sweep said portions of said beam through predetermined paths defining said area.

3. In a radio direction finding apparatus, means comprising an antenna for projecting a main beam of electromagnetic waves into a desired area, means for receiving echo waves from an object in the path of said beam, a first group of pivotally mounted planar reflectors positioned in the path of a first portion of said main beam and spaced from said projecting means for deflecting said first portion of said beam in one direction, a second group of pivotally mounted planar reflectors positioned in the path of a second portion of said main beam for deflecting said second portion of said beam in a second direction, controllable actuating means for continuously moving each of said groups of reflectors to sweep said portions of said main beam through predetermined paths defining said desired area, and means for moving the axis of said main beam to bring said axis into coincidence with a located object.

4. In a radio direction finding apparatus, means comprising an antenna for projecting a main beam of electromagnetic waves into a desired area, means for receiving echo waves from an object in the path of said beam, a first group of interconnected pivotally mounted planar reflectors positioned in the path of said main beam and spaced from said projecting means for defiecting a portion of said main beam in a substantially vertical direction, a second group of interconnected pivotally mounted reflectors positioned in the path of another portion of said main beam for deflecting said other portion of said beam in a substantially horizontal direction, separately controlled actuating means for continuously'moving said reflectors to sweep said portions of said beam through predetermined paths defining said desired area, and means for rotating said main beam in a conical path. having its apex in the region of said antenna to indicate the direction of displacement of a reflecting object from the axis of said main beam.

5. The method of indicating the position of a reflecting object in a. desired area which comprises projecting a main electromagnetic beam into said area, deflecting a fractional portion only of said beam to form a second beam at an acute angle to said main beam, continuously changing the direction of said deflection thereby continuously to sweep said second beam through a predetermined path definingsaid area, receiving irom said object an echo of said second beam, determining from said echo the direction of displacement of said object from the center of said main beam, and moving said main beam in accordance with said determination to bring said object into said main beam.

6. The method of indicating the position of a reflecting object in a desired area which comprises projecting a main unidirectional electromagnetic beam into said area, deflecting a tractional portion only oi! said beam to form a second beam at an acute angle to said main beam continuously changing the direction 0! said deflection thereby continuously to sweep said second beam through a predetermined path defining said area, receiving from said object an echo oi said second beam, determining from said echo the direction of displacement of said object from the center of said main beam, moving said main beam in accordance with said determination to bring said object into said main beam, and reducing the angle of sweep of said second beam to bring it entirely within said main beam and gradually to reduce said angle to zero while continuing to move said main beam in the direction'of said displacement thereby to bring the center of said main beam upon said object.

HOWARD I. BECKER.

REFERENCES CITED The following referencesare of record in the flle of this patent:

UNITED STATES PATENTS I Number Name Date 1,931,980 Clavier Oct. 24, 1933 2,083,242 Runge June 8, 1937 2,115,788 Scharlau May 3, 1938 2,133,615 Gerhard Oct. 18, 1938 2,231,929 Lyman Feb. 18, 1941 2,419,556 Feldman Apr. 29, 1947 FOREIGN PATENTS Number Country Date 497,147 Great Britain Dec. 9, 1938 

